Fatty acyl isethionates (e.g., cocoyl isethionates) surfactant “products” are defined as mixtures of anionic acyl isethionate surfactants and fatty acids/fatty acid soaps. They are highly desirable in personal care skin or hair cleansing products, particularly in personal care products, because they lather well, are mild to the skin and have good emollient properties. Typically, fatty acid isethionate surfactant products are produced by esterification of fatty acids or by reaction of fatty acid chloride having carbon chain length of C8 to C20 with isethionate. A typical surfactant product containing fatty acyl isethionate contains about 40 to 95 wt. % acid isethionate, and 5 to 50 wt. %, typically 10 to 40 wt. % free fatty acid, in addition to isethionate salts, typically at less than 5%, and trace (less than 2 wt. %) of other impurities.
A problem with the ready use of fatty acyl isethionate surfactant products in liquid compositions, i.e., composition wherein the acyl isethionate surfactant product is used as a primary component comprising a level of at least 50% wt. % of total fatty isethionate surfactant product and other synthetic surfactants in the liquid composition, however, is the low solubility of these compounds in water. This is especially true for fatty acyl isethionate surfactant product containing high level of free fatty acid/fatty soaps (10% by wt. or higher) and/or long chain fatty acyl isethionates component (e.g., C14 and higher). The fatty acyl isethionate component tends to form insoluble surfactant/fatty acids crystals, with the amount of crystals depending strongly on the storage temperature due to the wide range of dissolution temperatures of these crystals. This in turn results in unstable liquid cleansers which exhibit very thick or very thin consistency at low and elevated temperatures. At low temperature, the liquid composition becomes a semi-solid gel which is difficult to use. At elevated temperature, the liquid composition turns into water-thin liquid which causes phase separation of the product.
It would therefore be of tremendous advantage to have compositions having consistent viscosity at both low and elevated temperatures; as well as a way of manipulating compositional ingredients to ensure such consistent viscosity is obtained and that fatty acyl isethionate products, no matter what their free fatty acid/fatty soap content or their chain lengths, can be readily used as the primary surfactant in a liquid cleanser composition. It has not been readily apparent how to address the problem since there are probably hundreds of ways to increase or decrease viscosity but when the issue is one of maintaining a consistent viscosity, it is difficult to know where to begin. Unpredictably, applicants have found specific compositions which are stable (using high levels of polyol) and processes for making such compositions.
Applicants have now found that the problem of inconsistent viscosity and physical instability for liquid cleansers containing high level of fatty acyl isethionate surfactant products can be resolved by forming viscous surfactant liquid crystals at a temperature at or above the dissolution temperature of these long chain fatty acid and/or fatty acyl isethionate crystals such that the liquid composition has high enough viscosity to ensure stability, said stability being defined by the absence of visible physical separation after two weeks of storage at 45° C. Unpredictably, applicants have found the use of polyol, i.e., glycerin or sorbitol, at a level of at least 10 wt. % in the liquid composition, creates a more consistent viscosity which allows fatty acyl isethionate product, regardless of free fatty acid content or chain length of isethionates, to have more consistent viscosity at low and elevated temperatures and to be storage stable. As noted below in connection with EP 1237534, this is particularly unpredictable in that high level of glycerin has in other compositions, caused phase separation and instability.
Acyl isethionate liquids do exist in the art. U.S. Pat. No. 5,415,810 to Lee et al., for example, discloses compositions comprising fatty acyl isethionates and zwitterionic surfactant (e.g., cocoamidopropyl betaines). The reference does not appear to disclose the fatty acyl isethionate product of the invention (comprising 10 to 50% fatty acid) and, in fact, reference teaches away from use of fatty acids.
U.S. Pat. No. 5,739,365 to Brody et al. and U.S. Publication No. 2004/0224863 both disclose use of synthetic surfactants with ammonium counterion to help solubilize fatty acid isethionate.
U.S. Pat. No. 5,132,037 to Greene et al. (and related U.S. Pat. No. 5,234,619 and U.S. Pat. No. 5,290,471) disclose compositions with C8 to C22 acyl isethionates, synthetics, and free fatty acid, preferably C16 or higher. There seems to be no disclosure of high temperature stability problems associated with liquids containing high level of fatty acid acyl isethionate product or ways to solve such problems. As seen in Table 3 below, not all compositions are stable at 45° C. storage and it is unpredictable what would have been required to achieve such stability.
U.S. Pat. No. 5,952,286 and U.S. Pat. No. 6,077,816, both to Puvvada, disclose liquid cleansing compositions which may contain acyl isethionates and which comprise soluble, lamellar phase inducing structurant (e.g., branched fatty acid). There appears to be no disclosure of high levels of glycerol or any resultant benefit.
Liquid cleansing compositions containing high level of polyol are well known in the art for various purposes. U.S. Pat. No. 5,716,919 to the Andrew Jergens Company taught the use of polyols at a level of 25 to 80 wt. % in a nonionic surfactant-containing liquid cleanser to enhance the cleanser's mildness, non greasy and clean after wash feels. EP 1029532 of Unilever claims self-preserving liquid cleansing composition using high level of glycerol (30 to 50 wt. %) to lower water activity of the liquid composition. In EP 1237534 patent to Unilever, high glycerin content is desired in liquid cleanser for cleanser mildness. However, the patent showed that high glycerin content destabilized liquid composition comprising sulfosuccinic acid monoester surfactants (lines 5 to 9 page 2). To stabilize the liquid composition of this patent with high level of glycerin, a combination of fatty acid soap and acrylate copolymer was required.
U.S. Pat. No. 6,429,177 to Williams et al. describes a separating multi-phase personal wash composition containing 4 to 20% by wt. of polyol in the composition. The patent discloses polyol together with salt to destabilize liquid composition in order to form bi-phasic liquid cleanser. The use of glycerin as high temperature stabilizer is completely unpredictable.
Applicants filed in December 2006 three cases relating to liquid compositions with crystal modifier systems similar to those of the subject invention (U.S. Ser. No. 11/613,666; U.S. Ser. Nos. 11/613,696 and 11/613,617, each to Tsaur). There was no teaching or suggestion in any of these applications, however, that polyol alone at a level of 10 wt. % of more could be used or would function in compositions where fatty acyl isethionate surfactant product comprises 50% or more of the surfactant system by forming viscous surfactant liquid crystals upon the dissolution of fatty acyl isethionate/fatty acid crystals at elevated temperatures (40° C. or above); or that this would function to stabilize liquids at elevated temperature.
Applicants have also filed a related application, Ser. No. 11/850,159 on Sep. 5, 2007 in which combination of alkylamineoxide, alkylamidoamide or mixtures thereof and a second component (e.g., hydrocarbon oil, ammonium salt) form on elevated temperature stabilization system for acyl isethionate surfactant product. The glycerol stabilization system of the subject invention is not disclosed.
None of the references, alone or together, teach or suggest compositions comprising fatty acyl isethionate surfactant product or use of high level of polyols to provide compositions with product viscosity less sensitive to temperature and stable at elevated temperature storage conditions.